Telephone system



Aug. 9, 1927.

- 1,638,295 G. R. EATON ET AL musrnoma SYSTEM Filed Nov. 13. 192-2 2Sheets-Sheet 1 INVENTOES GEORGE KEA Y MICPAELB=STAZAK B ATTORNEY Aug. 9,1927. ,638,295

. G. R. EATON ETYAL TELEPHONE SYSTEM I Filed Nov. 15. 1922 2Sheets-Sheet 2 INVENTORS GEORGE R. EATON MICHAEL B. STAZAK BY ATTORNEYPatented Aug. 9, 1927.,

UNITED STATES PATENT OFFICE.

GEORGE E. EATON, OF OAK PARK, AND MICHAEL B.

ST'AZAK, OF CHICAGO, ILLINOIS,

ASSIGNOBS T0 KELLOGG SWITCHBOABID AND SUIEPLY COMPANY, OF CHICAGO,ILLINOIS, A CORPORATION OF ILLINOIS. I

TELEPHONE SYSTEM.

Application filed November 13, 1922. Serial No. 600,554.

Our invention relates to telephone systems, and more particularly tosystems in which a number of subscribers lines terminate in a privatebranch exchange and a number of other subscribers lines terminate in amain exchange of the manual type or of the automatic type ofswitchboard;

. An object of our invention isthe provision of an operators cordcircuit at the pri vate branch exchange for interconnecting subscriberstelephone lines, terminating therein, and also the provision of atwo-way trunk circuit between the private branch exchange and mainexchange, the said operators cord circuit of our invention adapted tooperate in connection with said trunk circuit to interconnectasubscribers line at the private branch exchange with a subscribers lineat the main exchange.

Another object of our invention is to provide battery for conversationalpurposes from the private branch exchange when our cord circuit is usedfor interconnecting subscribers lines terminating in the private branchexchange, but to provide battery for conversational purposes from themain exchange, instead of the private branch exchange, when connectionis madebetween the cord circuit at the private branch exchange and thetrunk circuit ofour invention.

Still another object of our invention is to place the supervisory signalat the main exchange. which notifies the operator thereat whenconversation has terminated under the control of the subscriber at theprivate branch exchange, so that when the subscriber replaces hisreceiver upon its switchhook the said supervisory signal will light toindicate to the main exchange operator that the subscriber at theprivate branch exchange has replaced his receiver. We also place asupervisory signal at the private branch exchange under the control ofthe subscriber thereat so that when he replaces his receiver upon itsswitchh-ook the operator at the private branch exchange will be informedthat the said subscriber has replaced his receiver at the same time themain exchange operator is notified of this fact. The features just setout above in this paragraph exist when the main exchange is a manuallyoperated exchange, and should the main exchange be' an automaticexchange, the autoexchange in a trunk I private niatic switches areplaced under the control of the subscriber at the private branchexchange, as is also the said supervisory signal at the private branchexchange.

A further object of our invention is the provision of means whereby thesubscriber at the private branch exchange may send a series of currentimpulses to operate the switches at the automatic exchange or that theoperator at the private branch exchange may send a series of currentimpulses to operate the automatic switches at the automatic exchangeinstead of-said subscriber.

Still another object of our invention is the provision of means wherebythe private branch exchange operator may be signaled over the trunkcircuit from themain exchange regardless of whether or not the saidtrunk circuit is engaged by a plug of a cord circuit at the privatebranch exchange.

Theabove features, as well as other features of our invention, will bemore particularly pointed out in the following specification and. in theappended claims.

For a more complete understanding of our invention, reference may be hadto the accompanying drawings, in which Fig. 1 illustrates thearrangement of our cord circuit, and

Fig. 2illustrates our trunk circuit having its one end terminating inthe private branch jack and night jack, and its other end terminating inan automatic switch, and also terminating in a trunk jack at main manualexchange. In actual practice, however, it will be understood that aseparate trunk circuit will extend to the automatic exchange and aseparate trunk circuit will also extend to the main manual exchange. I

Referring now in general to our invention. in 1 we show a substationhaving an impulse-sending device D and terminating in a jack J withwhich is operatively as sociated a. line signal S. The cord circuit Coi? our inv ntion which is provided for the branch exchange, comprises apair AP and GP interconnected bythe Y and Y, having the f plugs talkingconductors condensers K and K interposed. In the answering end of thecord circuit C is pro vided a generator G and a ringback key RK and alsoa slow-acting sleeve relay SR, an answering supervisory relay AR and asupervisory signal AS. The sleeve relay SR is adapted to energize whenAP is connected to a ack who e sleeve cont-act is connected to ground,and relay SR energizing places the supervisory signal AS under thecontrol of the answering supervisory relay AB. The calling end of cordcircuit C is provided with a slow acting sleeve relay SE, a callingsupervisory relay CR and a supervisory signal G5, which is placed underthe control of relay CR- when the sleeve relay SR is energized. Animpulse-send ing device 0-D and a key DK are provided for connecting thesaid device OD in circuit with plug Cir, as is also provided a ringinggenerator G and a rin ing key BK for connecting said generator to theplug GP. A listening key LK is provided for connecting the operatorstelephone set O to the conductors Y and Y of cord circuit C. Aslow-acting relay SCB is provided for con trolling the circuit of signalCS, said signal being either under the control of a subscriber at asubstation terminating in the private branch exchange or by the operatorat cord circuit C. I also provide the cord circuit C with relays BR, SGRand DR which will only operate when the cord circuit C is connected to atrunk circuit, but will not operate when the cord. circuit C isinterconnecting subscribers lines at the private branch exchange. To theright of Fig. 1 we show a substation B provided with an impulse-sendingdevice D and terminating in a jack terminal J which has associated withit a line signal S.

In Fig. 2 we show a trunk circuit TC terminating in a night jack NJ,which night jack NJ is used for the wellknown purpose in night service,and also terminating in a trunk jack TV} which is located at the privateb 'anch exchange. Associated with the trunk jack TJ is a relay 27 whichenergizes when a plug of a. cord circuit at the branch exchange isinserted into the jack TJ, said relay 27 controlling the lighting of thesupervisory signal TS. An alternating current relay AG is provided whichis controlled from the main exchange for causing the signal TS to lightto signal the private branch exchange operator even though a plug of acord circuit is engaging the jack TJ. A relay BB is also provided forcon trolling the circuit of relay 27 and operates when relays 27 and ACare energized. The other end of the trunk circuit TC terminates in atrunk jack TJ at a. main manual exchange, said trunk jack TJ having acutoil relay CO and a line relay LR associated therewith for controllinga. supervisory signal SS. The answering end of a cord circuit C at themain manual exchange having an answering plug AP, a ringing key RKsleeve relay SR supervisory relay AR and signal AS for the usualwellknown purposes, is shown and is adapted to be connected to the trunkjack TJ. We also show the said other end of the trunk circuit TCterminating in a non numerical switch F S, but this is only for thsakeof explanation, for in actual practice a separate trunk circuit T G willbe provided be tween the private branch exchange and automatic exchange,and a separate trunk circuit will also be provided between the saidprivate branch exchange and the main manual exchange. The switch FSoperates automatically, when a plug is inserted into the jack TJ, toselect an idle set of contacts 90, 91 and 92 leading to an idle selectorswitch. The said switch comprises an olinormal contact ON, a line relayLR and a cut-off relay CO, said relays Ll-land CO operating, whenconnection is made with the trunk jack TJ, to render the said trunkswitch busy against being selected when in its oif-normal posit-ion, andto also close a circuit through the motor magnet M to'cause the same tomore the wipers 87, 88 or 09 into engagement with an idle set ofcontacts 90, 91 and 92 leading to an idle selector switch.

and in case the switch FS is unable to select an idle selector switch.busy-back aicans BB are provided for notifying the calling sub scriberor operator at the private branch exchange of this fact.

Having referred to our invention in gen eral, we will now describe thesame more in detail, and for aclearer understanding will first describethe manner in which a connection is established by our cord circuitbetween two subscribers at the private branch ex-' change. Assuming thatthe subscriber at substation A initiates a call. by removing hisreceiver from its switchhook, the calling 1, na] S appearing before theoperator will light, over a circuit traced from battery. through thelamp S, normal contact 1 of jack J, line limb 2, through the now closedswitohhook contacts of substation A, line limb 3, normal contact 4 ofjack J to ground. The operator seeing the lighted lamp S will insert theanswering plug AP into the ack J and then operate the listening key LKto connect her telephone set 0 in conversational circuit with thecalling subscribers line, and will inquire the wants of the callingsubscriber at substation A. When the plug AP is inserted into the jackJ, an energizing cir cuitis established for the slow-acting sleeve relaySR, traced from battery, through the winding of relay SR, conductor 5.normal contact 6 of relay DR, conductor 7, sleeve contacts of plug APand jack J to ground, and relay SR energizing over this circuit, closesan energizing circuit for the answering supervisory relay AR, tracedfrom battery, through the lower winding of relay AR, alternate. contact8 of relay SR, ring conductor of cord circuit 0, normal contact ill) *relay DB, conductors 9 of ringing key RX, ring contacts 01" plug AP andjack J, through the alternate switchhook contacts of substation A, tipcontacts of jack J and plug AP, normal contact 10 of key BK, tipconductor and alternate contact 11 of relay SR, to ground through theupper winding of relay AR. Relay SR energizing closes a circuit for theanswering supervisory signal A3 at its alternate contact 12,v but si nalAS will not light at this tion is idle, the operator will insert thecalling plug GP into the jack J, whereupon a. circuit-is closed tortheslow-acting sleeve relay SR, traced rroin battery through the winding ofrelay SR normal contact 14: of

and 16, sleeve/contacts ot plug GP and jack J to ground. R elay SRenergizing closes its alternate contacts 17, 18 and 19, which closes acircuit for the calling supervisory relay CR, but relay CR will notenergize until the called subscriber responds. The calling supervisorysignal CS will light over a circuit traced from battery, through thesignal CS, alternate contact 18 of relay to ground at normal contact 20of relay CR, and remain lighted until the called subscriber respondstonotify the operator when the called su-b scribe-r answers. lheoperator now operates the ringing key BK to ring the call bell at thecalled substation B, and ringing current may be traced from thegenerator G, alternate contact 21 of ringing key BK, tip con tacts ofplug GP and jack J, through the call bell at substation B. ring;contacts of jack J" and plug P, alternate contact 22 to ground. When thecalled subscriber removes his receiver from its switchhook in responseto the call bell and the key 3K is in its normal position, relay CR willenergize and open its normal contact 20 in the circuit of signal CS,whereupon nal CS is etl'aced to notify the operator that the calledparty has responded and the operator will leave her ringing key BK inits normal position. The circuit for relay CR may be traced from batterythrough the lower winding oi relay CR. alternate contact 17 of relay SE,normal contact 23 of key DK, normal contact 22 of key BK, ring contactsof plug CP and jacl; J, through the now alternate contacts of the raisedswitchhook at subf ation B, tipcoiuacts of jack J and plug: Ci 7 lcontact 21 of key Bl. normal contact 2-l of key DK, alternate contact 19of relay SR, to

ground through the upper winding of relay CR. v

The subscribers at substations A and B are now in conversationalcircuit, which may be traced over the heavily marked conductors Y and Yof cord circuit C. When conversation is terminated, the subscribersreplace their receiv rs upon their respective switchhooks, and thesubscriber A replacing his receiver will open the circuit of relay AR,which relay, AR will de-energize and close the circuit for lamp AS,Whereupon lamp AS will light to notify the operator that the callingsubscriber has replaced his receiver, and when the called subscriber Breplaces his receiver, the circuit of relay CR will be. opened and relayCR will (ls-energize and close the circuit for the signal CS, causingsaid signal CS to light. The operator seeing the burning signals AS andCS, will know that conversation between subscribers A and B hasterminated and will withdraw the plugs AP and CP from the jacks J and J.respectively, whereupon the cord circuit is restored to normal and thesignals S and S are again placed under the control of the subscribers Aand B, respectively.

Having described the operation of our cord circuit C in establishing aconnection bet veen sul'iscribers at the private branch exchange, Wewill. now describe its operation. when connection is established betweena subscriber at the private branch exchange and a subscriber at a manualmain exchange.

Assuming now that the subscriber at substation A initiates a call anddesires to converse with a subscriber the "main er:- change, theoperator at cord circuit C will answer the call in the same manner asdescribed above, and the cord circuit will operate likewise in the samemanner. The operator learning that thecalling subscriber desires toconverse with subscriber at the main exchange, will insert the plug GPin the trunk jack TOT, thereby closing normally open contact 26 of jackTJ by ineans of the plug OP, which clues a circuit for the slow-actingrelay 27, traced from battery, through the winding of said relay 27,normal contact 28 of relay RR, conductor 29,.norma'l contact 30 oi"relay AC, conductors 3'1 and 32, alternate contact 26 at jacl-c Tel, toground. Relay 2? over this circuit attracts its lower armature 33 toprevent the contact member 34 from closing a: circuit for the tunksupervisory signal TS at this time, and also closes its alternatecontacts 35 and 36 to extend the tip and ring conductor of the trunkcircuit TC through to the main exchange Where they terminate in thetrunk jack TJ. The line relay LR in the line circuit at the mainexchange will now operate over a circuit energizing traced from groundthrough the Winding of the line relay LR, normal contact 105 of thecut-off relay CO tip conductor 38 of the trunk, normal contact 40 ofjack NJ, alternate contact 35 of relay 27, tip contacts of jack TJ andplug Cl normal con tact 21 of key BK, normal make-beforebreak contact 24of key DK, normal con tact 19 oi? relay SR (the said relay SR does notenergize when the plug CP is con nected to a trunk jack, as the sleeveof the jack TJ is free from ground and relay SR failing to energizerelay OR- is prevented from energizing,) conductors 42 and 43, alternatemake-betore-break contact 44 of relay SR, winding of relay BR, normalcontact 45 of relay DR. conductor 46, alternate make-before-breakcontact 47 of relay SR, conductor 48, normal contact 17 of relay SR.normal make-betore liu'eak contact at? of key DK, normal contact 22 ofkey 12K. ring contacts of plug GP and trunk jacl. TJ, alternate contact36 of relay 27, normal contact 41 of jack NJ, ring conductor 39, normalcontact 106 of relay CO and to battery through the other winding of theline relay LR at the main exchange. The line relay LR operating closes acircuit for the supervisory signal SS to denote to the main exchangeoperator that a call is awaiting her attention on the trunk line, saidcircuit being traced trom battery through the signal SS. alternatecontact 107 of relay LR to ground. Belay BR- will not energize over thecircuit just traced due to the high resistance of the line relay LR, atthe main exchange, and also due to the shunt circuit about relay BRwhich may be traced from point 82 in the above traced circuit, throughresistance R, normal contact 64 of key LK, normal contact 45 of relay DRand to point 83. The operator at the main exchange noting the burningsupervisory signal SS before her Will insert the answering plug AP of acord circuit C provided for her. into the outgoing trunk jack TJ toanswer the call. and upon the insertion ot said answering plug AP intosaid outgoing trunk ack T5, the sleeve relay SR Will operate and closeits alternate contact 108, and the cut-oft relay C9 associated therewithwill operate to cause the line relay LB to de-energize to el'tace thesaid burning signal SS in the wellknown manner. he battery now tedthrough the relay BR- ot cord circuit C, from the main exchange. throughthe windings of the supervisory relay AB in the cord circuit at the mainexchange, said windings being of such resistance to permit theenergization of relay BR, the circuit of relay BR being the same astraced above except as to the circuit at the main exchange, Which Willnow be through the Winding of relay AR instead of relay LR,

and a further description of this is not deemed necessary. Relay ARenergizing opens its normal contact 109 to prevent the prematurelighting of lamp AS. Relay BR energizing closes a circuit for the relayDR, traced from battery through the upper Winding of relay DR, conductor49, alt-ernate contact 50 of relay BR, sleeve contacts of plug AP andjack J to ground, and relay energizing closes a locking circuit foritself traced from battery through its upper Winding and alternatecontact 6, conductor 7, and to ground through the sleeve contacts of pluAP and jack J. Relay DR energizing opens the energizing circuit of relaySE at normal contact 6 of relay DB, and relay SR deenergizing opens itsalternate contacts 11 and 12, which ca ises relay AR to deenergize, andsaid relay SR tie-energizing also closes a circuit for the supervisorycontrol relay SCR, said circuit traced from ground at the main exchangethrough the Winding of the supervisory relay AR, the tip conductor 38 ofthe trunk circuit, normal contact 40ot jack NJ, alternate contact 35 ofrelay 27, tip contacts of trunk jack TJ and plug GP, normal contact 21of key 'RK, normal contact 24 of key DK, normal contact 19 of relay SR,alternate contact 53 of relay DR, Winding of relay SCR, normal contact11 of re lay SR, conductor 55, normal inakebeforebreak contact 44 ofrelay SR, Winding of relay BR, alternate contact 56 of relay BR, normalcontact 58 of relay SCR, conductor 46, normal makebefore-break contact47 of relay SR, conductor 59, normal contact 8 of relay SR, conductor48, normal Contact 17 of relay SR, normal contact 23 of key DK, normalcontact 22 of key BK, ring contacts of plug GP and jack TJ, alternatecontact 36 of relay 27, normal contact 41 of jack NJ, ring conductor 39to battery through the other Winding of the supervisory relay AF. in thecord circuit at the main exchange. Relay SCR energizing over thiscircuit opens its normal contact 58, Which opens the circuit of relayBR, and relay BR restores, and relay SCR also opens its normal contact60 to prevent the lighting of the supervisory signal CL. Relay BRde-energizing opens its alternate contact 56, there by opening thecircuit of relay SCR, but relay SUB Will not restore, as a circuit isclosed tor said relay SCR through the calling substantion A. The circuitmay be traced as above described up to and including normal contact 11,Where it extends over conductor 61, normal contact 10 of key BK, tipcontacts of plug AP and jack J, through the alternate SWltOllllOOlZcontacts of substation A, ring contacts 0t jack J and plug AP, normalcontact 9 of relay BK, normal contact 8 of relay SR, conductor 48 andover the previously traced circuit. Thus, it

lUtl

all)

cord 'circuit from "the 1 1 g1 ounu,

is seen that the supervisory"signal CS at cord circuit (l and that'thesupervisory .sig-

nal AS in the cord circuit .at the main ex change are contr l ed by thecalling subscriber, and when the calling subscriber A replaces hisreceiver upon its switchhook, the lamp GS of cord circuit C and thesuper visory signal at the main exchange will light to notify therespective operators that the connection is no longer desired.

The above operation talres place upon the main eI-Ichange operatorinserting the answering plug AP of the cord circuit into the outgoingtrunk jack TJ of the trunk line TC. The operator at the main exchange isnow in conversational circuit with the calling subscriber at substationA, which may be traced over the heavily marked conductors, talkingbattery being fed from the mainexchange, to the cord circuit C at theprivate branch exchange andcalling substation A and the main exchangepperator will inquire the wants or" the callihgsubscriber at substationA, and upon learning that he desires to converse with a subscriber atthev main exchange, she will establish connection with the calledsubscribers line and signal. him in the usual manner.

The calling subscriber and called sub scriber are now in conversationalcircuit and after conversation has terminated the subscribers rep-lacetheir receivers upon theii respective switchhoolrs. The calling subscribcr at substation A havingreplaced his receiver upon itsswitchhoolr, the circuit for the relay SCR- in the cord circuit C isopened and the circuit for AR in the cord circuit at the main exchangeis opened, and relay SCH restoring closes its normal contact 60., rebyclosing a circuit for the supervisory s1 l CS, traced from battery,through the 'uitl GS, normal contact '18 of rel SR, alternate contactDlhto ground at normal contact of relay SCH; Said signal CS lighting.over tlns circuit notifies the private branch exclia1ige operator thatconversation has terminated and that the calling subscriber has replacedhisreceiver, andishe will then withdraw'the plugs AP and P from jacks Jand J, respectivelywhereupon .the cord circult C normal position. Thesuperrela R at the mainexchange reimmediately upon the subscriber atsubstaion A replacing his receiver, closes u "for the. supervisorysignal AS, traced itrom battery, through said signal AS, normal contact109 of relay AR" to nd the main exchange operator observing this burni.0* signal AS, willfknow that the calling sub. riber has replaced hisreceiver and will withdraw the plug of her he outgoing end jack thesupervisory relay.

whereupon said relays restore,

54 of relay TJ of the trunk circuit TC at the main exchange.

It sometimes occurs that the calling subscriber notifies the operator atthe private LK after learning the wants of the calling 7 subscriber, butleaves it in its operated po-' sition for the purpose of preventing afalse disconnect signal to'be given to the main exchange operator.vVh'en the mainv exchange operator answers the call, a circuit is closedfrom ground through the winding of the supervisory relay AR at the mainexchange, tip contacts of plug AP and jack TJ. trunk conductor '38,normal contact 40 of jack NJ, alternate contact 35 of relay .27, tipcontacts ot jack TJ and plug GP,

normal contact 21 of key BK, normal contact 24 of key DK. normal contact19 of relay SR, conductors l2 and 43, alternate contact 44 of relaySR,winding of relay BR, alternate contact (i iof listening key LK,conductor 46, alternate contact 4.7, conductor lSy'normal contact 17 ctrelay SR, normal contact 23 of key DK, normal contact 22m" key RK, ringcontacts of plug GP and jack TJ, alternate contact 36 of relay 2?,normal contact 1-1 of jack NJ, conductor 39. ring contacts of jack TJand plug AP,

to battery through the other winding of the said supervisory relay A3 atthe main exchange. The supervisory relay at the main exchange operatesover this circuit to prelay DR energizing opens the circuit of re- SR,whereupon relay SR- restores as delay scribed above, but relay BR willnot restore when relay D R energizes, due to the fact thatmake-betorebreak contacts ll and 47 do not leave their alternateposition until after normal contacts 11 and 8 of relay SR are closed.whereby an operating circuit is maintained for the relay BR," saidcircuit being the same as described above. up to point 66loetweenconductors 42 and43, the circuit from thispoint-Qbeing through alternatecont-act 53-ot relay DR,.-winding of relay S'GR. rormal contact 1. 1 ofrelay SR, conductor It 3, normal contact 4a of relay SR, winding o1relay BR, alternate contact 64:

vent the lighting'ott the supervisory signal] i of listening key LK,conductor 46, normal contact 47 of relay SR, conductor 59, normalcontact 8 of relay SR, conductor 48, and the remainder of the circuit isthe same as traced above. Relay SCR operates over this circuit and opensits normal contacts 58 and 60, and the opening of contact 60 preventsthe burning of the supervisory signal CS. The operator at the mainexchange now converses with the private exchan e operator and upon beinginformed that connection is desired with a subscriber at the mainexchange, the main exchange operator will make connection with thecalled-tor sul scribers line in the usual. way, and when. the called-torsubscriber responds the private exchange operator will request him towait a moment until she rings the calling subscriber at substation A,which she does by operating the ring back key RE, which connects theringing generator G to the calling line to ring the call bell at thesubstation A. The calling subscriber at substation A will now respond tohis call bell by removing his receiver whereupon he will be inconversational circuit with the called-tor subscriber at the mainexchange. The private exchange operator upon hearing the callingsubscriber talk will restore her listening key LK which opens itsalternate contact 6%, thereby opening the circuit of relay Bit, and thenormal contact 58 of relay SCR being open, relay BR will restore, butrelay SCR will not restore since a circuit is now closed through thealternate closed contacts Off the switchhook at substation A and is heldenergized over the same circuit as hereinbefore traced. Whenconversation has terminated and the subscribers hang up their rcceivers, the supervisory signal CS at the private branch exchange andthe supervisory signal AS at the main exchange will light to notify therespective operators that conversation has terminated, whereupon theoperators will take down the;connect1on and the system will restore tonormal in the same manner as pointed out above.

Assuming now that conversation has terminated and that the subscribershave replaced their receivers and that the private branch exchangeoperator fails to withdraw the plug GP from the trunk jack TJ and thatthe main, exchange operator de sires to use this trunk to signal theprivate branch exchange operator. she may do so even through the plug GPremains in the trunk jack TJ, and the manner in which it may be donewill now be described.

The main exchange operator will operate the ringing key RK which willopen normal contacts 110 and 111 and close alternate contacts 110 and111 to connect ringing current to the tip and ring contacts of plug APto bring about the operation of relay AG at the private branch exchange,over a 67, condenser C, through the winding of al ternating currentrelay AG, normal contact 41 of jack NJ, conductor 39, ring contacts ofjack TJ and plug AP through ringing key RK to ringing generator and toground.

Relay AG operates over this circuit and attracts its armature 68 topermit the contact member 84 to engage the ground contact 69 when relay27 restores, said relay AC also closes its alternate contact 30, whichcloses a circuit for relay RR, traced from battery through the windingof relay RR, conductor 70, alternate contact 71 of relay 27, which relay27 is energized since the plug OP is still in the jack TJ, alternatecontact 30 of relay AC, conductors 31 and 32 to ground at alternatecontact 26 of jack TJ. Relay RR energizing closes a locking circuit foritself, through its alternate contact 72, con ductor 32 and to ground atalternate contact 26 of jack TJ, and also opens the circuit of relay 27at normal contact 28 of the said relay RR. Relay 27 now restores topermit the contact member 34 to engage the ground contact 69 to bringabout the lighting of the trunk signal TS before the private branchexchange operator, over a circuit traced from battery through the lampTS and to ground through the now closed contact member 34 and contact69. The private branch oporator observing the lighted lamp TS willwithdraw the plug OP from the jack TJ, which permits the spring contact26 to re store, thereby opening the locking circuit of relay RE, whichwillrnow restore, and then insert the answering plug AP and throw herlistening key LK to enable her to converse with the main exchangeoperator, thetalking battery being provided over the trunk circuit fromthe main exchange. When the plug AP was inserted into the trunk jack TJa circuit was closed for relay 27, which relay 2? energizes to eifacethe signal TS as described in the foregoing specification, and a circuitis also closed for relay BR, traced from ground throughthe winding ofthe supervisory relay AB, in the cord circuit at the main exchange,conductor 38, normal contact 10 and alternate contact 35, tip contactsof jack TJ and plug AP, normal contact 10, normal contact 414 of relaySR, winding of relay BR, normal contact 4 5 of relay DR, normal contact47 of relay SR, normal contact 9, ring contacts of plug AP and jack TJ,alternate contact 36, normal contact 4-1, conductor 39 and through thewinding of the said supervisory relay at the main exchange to battery.The supervisory relay AR at the main exchange energizes over thiscircuit to pre- Vent the premature lighting of the supervisory signal ASthereat, as before deto normal conta; ll of relay SB, whe

57 of relay BR, conductor 16, to ground,

through the sleeve contacts of plug GP and jack 5, and relay DRenergizing closes a locking circuit for itsel1 through its alternatecontact let and conductor 16 to ground at jack J. Relay DR energizesupon the insertion of the plug OP into the jack J before relay SR hastime to energize, and relay DR energizing opens its normal con tact 14:which prevcntsrelay SE from enerizing. Relav SCR does not 0 aerate atthis D time. The operator now operates the ring 1 ing key BK toapplyringing current to the call bell of the substation A and the subscriberin response to his call bell will remove his receiver from itsswitchhoolr, there by closing a circuit for relay SOB traced over thesame ci *it as that relay i up cattery now flows through the winding ofrelay SUE, alternate contact 53 of relay DR, normal contact 19 of relaySR, normal contacts 2a and 21, tip contacts of plug Cl? and acl: J,through the alternate switchhool: contacts of substation A, ringcontacts of jack J and plug GP, normal contacts 22 and 23, normalcontact 1'? of relay SR, conductor 48, normal contact 8 of relay SR andover the viously traced circuit of relay BR. Relay operating opens itsnormal contact 58, thereby opening the holding circuit ofrelay and relayBR restores if the operator has restored her ringing key BK, but thesupervisory relay at the main exchange held energized now in circuitwith the relay SCH. During the time the operator is ringing thecalledior subscriber at substation A, the supervisory signal GS willburn and when the lrey BK is restored and should the subscriber respondduring this period, relay SCR will energize as just pointed out above,and will open its normal contact 60, where; by the signal CS iseli'aced, which will notify the operator that the subscriber hasresponded.

The subscriber at substation A and the operator at the main exchange arenow in conversational circuit, talking battery being fed from the mainexchange over the heav ly marked conductors, and when conversation hasterminated the subscriber at substation A. replacing his receiver willopen the circuit of the relay SCR in the cord circuit C and of thesupervisory relay AR at the main exchange, thereby causing the lamp CSto light to notify-the operator at cord circuit C that conversation hasterminated and the operator at cord circuit C will take down theconnection, and after conversation has ninatcd the main exchangeoperator will raw the. plug AP from the jack: TJ, eupon the systemrestores to normal as described above. Should a subscriber at the mainexchange desire to talk with the subscriber at substation A at theprivate branch,

exchange the main exchange operator will,

insert the calling end of her cord circuit C shown on the draw1n as 1tis not deemed necessary tor a clear understanding) into the jack TJ andapply ringing current to operate'relay AC to bring about thell9'lltlllQ' of si nal TS as Jointed out above. In this instance therelays SCR and ill! will be energized by battery provided thro gh thesupervisory relay in the calli end of the cord circuit C, and whenU'scriber substation A replaces his r, the supervisory signal controlledby a (l relay in the said calling end will light to notify the mainexchange operator that conversation has terminated, whereupon she willtal-:e down the connection, and theoperator at cord circuit will benotified of the termiinition of conversation as polntedout above.

From the above description of our invention, i is at once clear that themain exchange operator may use the trunk circuit to signal the operatorat the private branch exchange, even though the plug of the cord circuitC remains 1n the trunk Jack TJ, and

further that the operator at cord circuit C.

and the operator at the main exchange will be notified that conversationhas terminated iruiiecuatelyupon the subscrlber at substai n It;replacing his receiver upon its switch-' branch exchange with acalled-for subscriber at an automatic exchange. v

Assuming that the calling subscriber at rue substation A of the privatebranch exchange-initiates a call, the private branch exc= nge operatorwill answer the call in the 'san'ie manner described in the foregoingspecification, and upon learning that the calling suhsc iber desires toconverse with a subscriber whose line terminates in an automatic er-rchange. she will insert the calling plug OP (it th cord circuit G into thetrunk jack TJ, it be. SSPil'iDlQfl now that the trunk circuit terminatesin an automatic exchange instead of a manual main exchange as decribedabove, whereupon relay 27 will energize to prevent the lighting of thesuper visory lamp TS, as was clearly pointed'out being had to thispatent for a clearer understanding of the operation of the switcheswhich. may not be understood from the en suing specification. When thealternate contacts and 36 of relay 27 are closed a circuit isestablished from battery through the winding of relay LR, wiper 89,normal contact or relay CO, conductor 39, normal contact 4-1 of jack NJ,alternate contact 36 of relay 2?, ring contacts of jack TJ and plug GP,normal contacts 22 and 23, normal contact 17 of relay SR, conductor 48,alternate contact 47 of relay SR, conductor 46, normal contact 45 ofrelay DR, through the winding of relay BR, alternate contact l t ofrelay 9ft, normal contact 19 of relay SR, normal contacts 24 and 21, tipcontacts of plug GP and jack TJ, alternate contact 35 of relay 2?,normal contact 40 of jack Nil, conductor 38, normal contact 81 of relayCO, wiper 88 and to ground. Relay LR energizes over this circuit butrelay BR does not energize over this circuit due to the high resistanceof relay LR compared with that oi? relay BR, and also due to the shuntcircuit about relay BR which may be traced from the point 82 in saidcircuit, through resistance R, normal contact 6a of listening key Lil:to point 83, and relay LR energizing closes its alternate contact 84 toplace a ground upon the conductor 95 to render the switch FS busy toprevent the switch FS from being selected while busy, and also toestablish an energizing circuit for outo'tl' relay CO through normalcontact ON. Relays LR and CO being energized a circuit for motor magnetM is established through their alternate contacts 85 and 86,respectively, whereby said magnet M advances wipers S7, 88 and 89 intoengagement with the first set of contacts 90, 91 and 92, which we willassume, leads to a busy first selector switch. Therefore, the testcontact thereof is grounded due to the busy condition of the firstselector switch, which may be more clearly understood by referring tothe Winston Patent No. 1,197,989, referred to above, and a lockingcircuit for relay LB and is, therefore, established, which may be traced"from ground at the test contact 90, test wiper 87, and alternatecontacts 93 and 94; and the windings of relay LR and CO, respectively.Relay CO thus maintains the circuit of driving magnet M closed,notwithstanding the opening of the circuit at 01]?- normal contacts Ollat the first step of the ductor another step and in tact continues suchadvancement until the test wiper 87 engages an idle test contact 90,which, we will assume, is the third one leading to a first selectorswitch. Assumin this is idle, as stated, it would be ungrounucd andtheretore the locking circuit tor relays LR and CO is interrupted, butrelay Llt being a slow-acting relay maintains its armature attracteduntil a locking circuit from the selected first selector switch isprovided, in the manner well-known in the art, but relay CO being aquick-acting relay immediately releases its armature, opening itscontact 89 in the circuit of driving magnet hill, thus rendering theswitch wipers inert, thereby permitting them to remain in engagementwith the contacts 0'1 the idle selector switch. W hen an idle selectorswitch is selccted,battery will be fed through the windings 01 animpulse relay in the selector switch to the contacts 91 and 92 engaged lthe wipers 88 and 89, respectively, windings of said impulse relay beingof such resistance as to permit the energization of the relay BR oyerthe previously traced circuit, and relay BR energizing a circuit will beestablished for relay DR,

traced from battery through the upper winding of said relay DR,conductor 49, alternate contact 50 of relay Blt to ground through thesleeve contacts of plug AP and jack J. Relay DR energizing over thiscircuit will lock up through its alternate contact 6, con- 7 and toground at the sleeve of jack J, and relay DR also opens the'energizingcircuit of relay BR at norn'ial contact l5 and closes a circuit forrelay SCR, said circuit being traced from the tip contacts of in thewell-known manner, the

till

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the jack TJ and plug GP, which battery extends to said jack TJ from thewiper 88,

through the normal contacts 21, 24: and 1 alternate contact 53 of relayDR, winding of relay SCR, normal contact 11 of relay SR, said relay SRhaving restored when relay DR energized, normal contact 10, tipeontacts'ot plug Al? and jack 5, through the now closed alternatecontacts of the switch hook at substation A, ring contacts of jack J andplug AP, normal contact 9, normal contact 8 01 relay SR, conductor d3,normal contact 17 of relay SR, normal con-l visory signal CS to preventthe same from lighting at this time. I

The operation of the finder-switch and the cord circuit C asustdescribed above lielay OCR energizing f occurs immediately upon theinsertion of the plug Cl into the jack TJ and before the callingsubscriberhas time to Operate his impulse dial D. The calling subscriberat substation A now operates his dial to send impulses to operatetheautomatic switches at the main exchange in the usual V6115.

known manner.

oeing from the Wiper 88, normal contacts 81 and 40, alternate contact 35of relay 27, tip contacts of jack TJ and plug CP, normal contacts 21, 24and i9, cOnduct' reQ, normal i contacts or jaclr ,J and plug AP, normalcontacts or plug contact 36 of relay 27, normal contacts 41- Contact 9or key RK, nor1nal contact 8 of relay SR cOnductOr, 48 normal contact 17of relay SR normal contacts 23 and 22, ring CP and jack TJ, alternateand SQand' to the wiper 89, When the dial i o erat d this ircuit will beo ened and clos'echas is well know but relay SCR being slow-actingwilinot de-energize, as' the circuit is openedandclosed at such rapiditythat the circuit will not; be opened sufficiently long to cause thede-energiz1ation of relay SCH, thus preventing the premature light ingor the signal CS. vAfter thev sending of the impulse and the calledsubscriber responds", it being assumed that the called sub scribers linewas idle when called, the calling subscriber at substation A and thecalled subscriber at the automatic exchange are in conversationalcircuit, traced over the heavily marked conductors having the condensersK and K" nterposed, talking battery being fed from the automaticexchange.

After conversation has terminated, the subscribers replace theirreceiversupon their respective switchhooks, and the replacing of thereceiver upon its switchho'ok at the sub station A Willopenthe circuitof relay SCR at the alternate switchhookcontacts of substation A,whereupon relay SCH Will restore and close its normal contact 60,thereby closing a circuit for the signal CS, traced from battery throughthe lamp CS, alternate contact 18 of relay SR, alternate contact 54 ofrelay DR to ground through horm'alcontact 60 of said relay SCR, YVhenthe subscriber at substation A replaces his receiver, the holdingcircuit for the automatic switches at the automatic exchange was opened,whereupon said switches restore in the usual and well-known I manner,The private branch exchange operator seeing the burning signal CS willknow that the conversation has terminated and thatthe calling subscriberhas replaced hi s rece1ver upon its switchhoolr, and she will Withdrawthe plugs Thec rcuit for the impulses v AP and CP from the jacks J andTJ, respeetivel whereupon relay DR restores and the signal CS isefia'ced and the cord circuit C is restoredto normal. Upon the removalof the plug CP hem the jack TJ, relay 27 restores as described in theforegoing specification, Now, as to the restoration of the switchFS,"this is effectedupon the restoration of the selector switch selectedby said switch' F S, which opens the holding circuit of relay LRandcauses relay'LR to restore. Relay LR restoring, its normal contact 84is closed, connecting ground through alternate contact ON and thewinding of relay CO to battery. Thus, relay LR being de-energized andrelay CO energized, the retaining pawls controlled by these [relays aredisengaged from thifr associated ratchet, allowing the switch ES torestore, The restoration or the switch and the other switches at theautomatic exchange may be understood more clearly by referring totheWinston patent n ioned a Reverting now to when the operator at cordcircuit" answered the calling subscriber at substation A, and assumingthat the calling subscriber thereat requested the operator to call thesubscriber at the automatic exchange to call him b ck when the calledforsubscriber answers, the callingsubscriber in this instance willreplace'his receiver, after informing the operator of his wants, andawaita call from the operator at cord circuit C v The operator willnotrestore her listening key at this time but will leave itin itsoperatedjposition to close its alternate contact 64; to close a circuit for therelay BR as her'einbef'ore described. The operator willnow insert thecalling plug CP into the jack TJ, Whereuponan idleselector switch isselected by the switch FS in the same manner pointed out above, and whenan i dle'select'or switch is selected an enerrgizing circuit is closedfor relay BR, as

hereinbefore tracechand relay BR energizing closes a circuit t9 bringabout the enerlz'ation 'f relay DR, and relay energizi'ng causes therestoration of relay SR as l ar y Poin d 1 1 abor e else the energizatjoof rel'ay SCH], the circuit for relay being the same as traced above upto normal contact ll where it now extends h o g orm l. when 4 o r ywinding of relay B R alternate contact 64 of key LK', conductor 45,normal contact 8 of relay e cla e the previously traced cir- Quit-- RelaSQR energi ing opens its contact 58 in the holding circuit of relay BR,

rela BB does not restore since the listening key LK is thrown and itsalternate contact Gels closed" to establish a holding circuitforrelayBR. Relay SCH energiz lag also prevents the eighties from lightia i cam h er e? n w. pe-'- ates her dialing lay DK, ninety ripening thecircuit of relays BB. and SCH, causing the same to restore, but whoserestoration has no particular effect at this time, said key DKconnecting the operators in'ipulse-sending device OD in circuit with thetrunk conductors leading to the automatic switches in the automaticexchange. The operator will now operate the impulse dial OD to bringabout the operation of the automatic switches at the automatic exchangeto cause the same to connect to the called-tor subscribers line, andhaving sent the required number of impulses, she will restore herdialing key DK, whereupon relays BR and SCR will again energize, andupon hearing the response of the called-tor subscriber, will inform himto wait until she rings the calling subscriber at substation A, whichshe will do by operating her ringback key BK, as here nbefore described,and upon hearing the calling subscriber answer she will restore herlistening key LK. The calling and called subscriber are now inconversational circuit. hen the listening key LK is restored relayBRde-energizes due to its circuit being opened at alternate contact 64:of said key LK, but relay SCR will not deenergize as it will now beheldv up over a circuit extending through the now closed alternateswitchhook contacts at substation A, and signal CS will not light, aspointed out above.

hen the conversation has terminated and the subscribers replace theirreceivers, the holding circuit for the automatic switches will be openedto permit the same to restore and relay SCR will restore and the signalGS of cord circuit C will light to denote that the calling subscriberhas replaced his receiver and the operator seeing this light willwithdraw the plugs AP and GP, wliich will bring about the restoration ofthe system as set out above.

In connection with the finder switch FS, means are provided to indicateto the calling subscriber or the private branch operator at cord circuitC when such switch has not been able to find an idle trunk. Forinstance, if all of the trunks leading from contacts 90, 91 and 92 arebusy, their test contacts 90 will be grounded, causing the switch tostep to the last set of contacts 90, 91 and 92. There being no groundconnected to terminal 90, relay CO immediately de-encrgizes but relay LRmaintains its armature attracted due to its slow-acting construction, sothat upon the closing of normal contacts 80 and Slot relay G0, a lockingcircuit LR is established from ground through busyback BB. terminal 91,wiper 88, normal contact 81. of relay CO, over the trunk conductor 38 tothe calling substation A, if subscriber thereat has not replaced hisreceiver, or through the listening key LK and the iii in its operatedposition, returning over the trunk conductor 39, normal contact 80,

relay CO, wiper 89, contacts 92 and 90, .wiper 8. alternate contact 93of relay LE to battery. A characteristic signal is thus transmitted frombusyback signal BB over the path just described, whereby the subscriberat A or the operator at cord circuit C receiving such signal. knows thatall of the trunks are busy and it received by the calling subscriber hewill replace his receiver, whereupon lamp AS will light to give anindication to the operator at cord circuit C, and the operator seeingthe burn ing lamp AS will withdraw the plug AP and GP from jacks J andTJ. The lamp AS lights when the subscriber at A replaces his receiverdue to the fact that relay SR remains energized since no idle selectorswitch was selected and relay AR will restore, thereby closing anoperating circuit for said signal AS. It the operator at cord circuitreceives the signal due to the fact that she has her listening keyoperated when she is requested by the calling subscriber to call thecalled-for subscriber, she will recognize the busy condition andwithdraw the plugs AP and GP, whereupon the switch FS will restore tonormal in the same manner described above.

Assuming now that a subscriber terminating in the automatic exchangedesires to signal the private branch exchange operator at cord circuitC, and that the plug OP of cord circuit C is still engaging the trunkjack TJ, which maintains the circuit of relay 2T closed, and that theswitch FS is in its normal position, the said subscriber will operatehis impulse sending device to cause a connector switch to engagecontacts connected to the conductors 95, 96 and 97, whereupon analternating current willv be sent from the connector switch overconductor 96, normal contact of jack NJ, conductor 67, condenser C,winding of re lay AC, normal contact ll of jack NJ, conductors 39 and 97to the connector switch at the automatic exchange. The relay AG operatesover this circuit and the relay 27 being energized due to the fact thatplug OP is in ack TJ, a circuit is closed through relay which energizesand closes a look ing circuit for itself. said relay energizing opensthe circuit ot relay 27 which will now restore to permit the lamp TS tolight as hereinbet'ore clearly set out. The operator seeing the lightedlamp TS will take care of the call by removing the plug CP and insertingthe answering plug AP into the jack TJ and will then extend the call asbefore described. Thus, it will be understood that the fact that theplug remains in the jack TJ after the conversation has termi- *sesessnated, does not prevent the trunk circuit TC from being used to signalthe private branch exchange operator at cord circuit C.'

lVhile we have illustratedand described a particular arrangement ofourinvention, it is to be understood that We do not wish to be limitedto the exact arrangement as shown and described, as modifications andchanges will suggest themselves to those skilled in the art, but weintend to cover all that which comes within the spirit and scope of theappended claims. 7

Having described our invention what we claim as new and desire to secureby Letters Patent is: V

1. In a te ephone system including a private branch exchange,subscribers telephone lines terminating therein, a link Cir-- cuit forinterconnecting said telephone lines inconversational circuit, a mainexchange, a trunk circu t between said private branch exchange and saidmain exchange. said link circuit adapted to be connected to said trunkcircuit to connect a subscribers line at the branch exchange with themain exchange, individual supervisory means at the main exchange and atthe private branch exchange controlled over the said sub'scribei"s'telephone line on either incoming or outgoing calls, to notify theoperators at the private branch exchange and main exchange re-sspectively when conversation has terminated,

means whereby the'subscriber on said tele-' phone line may communicatehis wants to the operator at the main eticl a'nge, or where- 4 by theoperator at saidbranch exchange may conununicatc said subscribers wantsto the mam exchange operator. means operative when said branch exchangeoperator .connnunicates the subscribers wants to the main exchangeoperator to prevent the said supervisory means operatingzto signal afalse disconnection signal upon the replacement of the callingsubscribers receiver upon its switchhooh while said subscriber iswaiting for his call to be completed, means for p'ro vidi batter; fortalking purposes from the int. i circuit to permit signalling of thebranch exchange operator shouid said link circuit remain connected tosaid trunk circuit. I I

In a telephone system including a private branch exchange and a main exi we. telephonelines terminating in said pri ate branch exchange, atrunk circuit beween said exchanges, a link circuit for interconnectine"said telephone lines and for connecting one of said telephone lines incircuit with said main esch'angeover said trnnl-r circuit, supervisorymeans at the main euchanee and at the private branch exchange controlledover said telephone line connected in circuit with said main exchange toindicate to the operator at saidrmain exchange and said private branchexchange when conchange may c'ommum "wants to the main exchangeoperator, means operative when said branch exchange opcratercommunicates thesubscribers wants in exchange, and means for said trunkchange, a linlr circ nectiori is no longer desired with said maineXchange on either incoming or outgoing 1 to the operator atthe' mainexchange, or

whereby the operator at said branch eX "cate said subscribers to themain exchange operator to prevent the said supervisory means operatingto signal a false disconnection signal upon the replacement of thecalling subscribers receiver upon its switchhook while said subscriberis waiting for his call to be completed, and means for said trunkcircuit for signaling the private bra'nchexchange operator over saidtrunk circuit regardless of whether or not the saidlink circuit isconnected to said trunk circuit. I

3. In a telephone system including a private branch exchange havingsubscribers telephone lines terminating therein, a link circuit forinterconnecting said lines, a main exchange, a trunk circuit terminatingin said private branch exchange and said main exchange, said linkcircuit adapted to be con nected to said trunk circuit to connect a subscriber on one of said telephone lines in conversational circuit withsaid main exchange,

supervisorymeans for said mainexcha'nge and said private branch exchangecontrolled over thesub'scrili efls line which is inconversa'tionalcircuit with the main exchange to notify the'privatebranch exchange operator and" main exchange operator when theconve'sational circuit is no longer desired on either incoming oroutgoing calls, means wherebyth'e subscriber on said telephone line maycommunicate his wants to the operator atl'he main exchange, r wherebythe operator at said branch exchange ma communicate said su'b's'criberswants to the main exchange operator, means operative when said branchexchange operator communicates the subscribers wants to the mainexchange operator to prevent the said supervisory means operating tosignal a false disconnection signal upon, the TGPlRCQH'HEHtof the calin; subscribers receiver upon its switchhook whilesaid' subscriber iswaiting for his call to be completed, means for providing tall:- ingbattery. from the main exchange, and

automatic means for said trunk circuit for signaling the private branchexchange op- 4. In a telephone system including main exchance a rivatebranch exchange having subscribers telephone lines terininating;-

therein, a trunk circuit terminating in said private branch exchange andsaid main ex- I v U I H at the private branch exchange for'ccnnectmg oneer said sub scribers" lines in circuit with said main exchange over saidtrunk circuit, individual supervisory means for said private branchexchange and said main exchange, and means controlled by the subscriberat the private branch exchange for controlling said individualsupervisory means on either incoming or outgoing calls for signallingfor a disconnection at both. exchanges, means whereby the subscriber onsaid telephone line may communicate his wants to the operator at themain exchange, or whereby the operator at said, branch exchange maycommunicate said subscribefls wants to the main exchange operator, meansoperative when said branch exchange operator communicates the subscribers wants to the main exchange operator to prevent the said supervisorymeans operating to signal a false disconnection signal upon thereplacement of the calling subscribers receiver upon its switchhookwhile said subscriber is waiting for his call to be completed, and meansfor said trunk circuit to permit the signalling oi the private branchexchange should said link circuit remain connected to said trunkcircuit.

5. In a telephone system including a private branch exchange and a mainexchange, a trunk circuit terminating in said branch exchange and saidmain exchange, a subscribers telephone line terminating in said branchexchange, a cord circuit for connecting said telephone line to saidtrunk circuit, individual supervisory signalling means for said mainexchange and said private branch exchange, said means controlled by thesubscriber at said private branch exchange on either incoming oroutgoing calls for inclicating termination of conversation at bothexchanges, means whereby the subscriber at said private branch exchangemay commun-icatc his wants to the operator at the main exchange, orwhereby the operator at said branch exchange may communicate the saidsubscribers wants to the main exchange operator, means operative whensaid branch exchange operator communicates the subscribers wants to themain exchange operator to prevent the said supervisory means operatingto signal a false disconnection signal upon the replacement of thecalling subscribefis receiver upon its switchhook while said subscriberis waiting for his call to be completed, and means for said trunkcircuit for permitting the operator at said cord circuit to be signalledfrom said main exchange regardless of whether or not said cord-circuitis connected to said trunk circuit.

6. In a telephone system including a private branch exchange havingsubscribers telephone lines terminating therein, a main exchange, atrunk circuit between said private branch exchange and said main exchange, a cord circuit for interconnecting said telephone lines and alsofor connecting any one of said lines to said trunk circuit, means forproviding talking battery from said main exchange, supervisory means forsaid cord circuit for indicating to the operator thereat when thesubscriber has terminated conversation, supervisory means at said mainexchange for indicating when said conversation has terminated, both ofsaid supervisory means being controlled by the subscriber at the privatebranch exchange on either an incoming or an outgoing call, means wherebythe subscriber at the private branch exchange may communicate his wantsto the operator at the main exchange, or whereby the operator at thebranch exchange may communicate to said subscribers wants to the mainexchange operator, means operative when said operator communicates thewants of the subscriber to the main exchange operator to prevent thesaid supervisory means operating to signal a false disconnection signalupon the replacement of the calling subscribers receiver upon itsswitchhook while said subscriber is waiting for his call to becompleted, and means for signalling the branch exchange operator fromthe main exchange prior to the disconnection of said cord circuitefromsaid trunk circuit.

7. In a telephone system, a private branch exchange, a subscriberstelephone line terminating therein, a main exchange, a trunk circuit forinterconnecting said exchanges, a

cord circuit at the private branch exchange for connecting saidtelephone line to said trunk circuit, means whereby the subscriber onsaid telephone line may communicate his wants to the operator at themain exchange, or whereby the operator atsaid cord circuit maycommunicate said subscribers wants to the main exchange operator, meansfor recalling said subscriber when the main exchange operator fulfillsthe wants of said subscriber, means for providing talking battery fromsaid main exchange, and supervisory means at the main exchange and atthe private branch exchange controlled over said telephone line oneither incoming or outgoing calls for notifying the respective operatorsthereat when the subscriber on said telephone line replaces his receiverupon its switchhook and to signal for a disconnection, means forrendering said supervisory means inoperative when the subscriberreplaces his receiver upon its switchhook while waiting for the operatorat the private branch exchange to communicate his wants to the mainexchange operator, and means for said trunk circuit to permit thesignalling of the branch exchange should said link circuit remainconnected to said trunk circuit.

8, In a telephone system including a via a vate branch exchange,subscribers telephone lines terminating therein, a cord circuit forinterconnecting said telephone lines, a main exchange, a trunk circuitfor interconnecting said exchanges, said cord circuit adapted to beconnected to said trunk circuit to extend a call from the private branchexchange to the main exchange, means whereby the subscriber at saidtelephone line may communicate his wants to the operator at the mainexchange, or whereby the operator at said cord circuit may communicatesaid subscribers wants to the main exchange op erator, means forrecalling the calling su scriber when the branch exchange operatoreffects the call to the main exchange, means for providing talkingcurrent'from the main exchange, individual supervisory means for saidprivate branch exchange and said main exchange controlled by thesubscriber at the private branch exchange on either incoming or outgoingcalls for indicating to the operators at said exchanges whenconversation has terminated, means operative when the operator at theprivate branch exchange er"- fects the subscribers call to the mainexchange to prevent the supervisory means operating to signal a falsedisconnection signal when the subscriber replaces his receiver upon itsswitchhook while waiting for his call to be completed, and means forsaid trunk circuit to permit the signallng of the branch exchange shouldsaid link circuit remain connected to said trunk circuit.

Signed by us at Chicago, in the county of Cook and State of Illinois,this 9th day of November, 1922.

GEORGE R. EATON. MICHAEL B. STAZAK;

